Python - matching a string within a string explicitly

Question

I am trying to match specific router interfaces. However, I am finding the below confusing, when searching for specific interface numbers, it is matching on the first condition, when i think it should be matching on the second condition:

string = ["TenGigE0/0/0/0.12", "TenGigE0/0/0/1.46", "TenGigE0/0/0/15.55"]

for item in string:
    if 'TenGigE0/0/0/0' in item or 'TenGigE0/0/0/1' in item:
        print("Yes")
    elif 'TenGigE0/0/0/15' in item:
        print("cool")

Output is:

Yes
Yes
Yes

How can i fix this?

This is because "'TenGigE0/0/0/15.55" and "'TenGigE0/0/0/1.46" starts with "'TenGigE0/0/0/1". — Captain'Flam
– Captain'Flam, Commented May 5, 2021 at 16:02

funie200 · Accepted Answer · 2021-05-05 16:02:23Z

1

Change the if-statements around:

string = ["TenGigE0/0/0/0.12", "TenGigE0/0/0/1.46", "TenGigE0/0/0/15.55"]

for item in string:
    if 'TenGigE0/0/0/15' in item:
        print("cool")
    elif ('TenGigE0/0/0/0' in item) or ('TenGigE0/0/0/1' in item):
        print("Yes")

Will get you:

Yes
Yes
cool

Since TenGigE0/0/0/15 contains TenGigE0/0/0/1 too, and if you check for TenGigE0/0/0/1 before checking for TenGigE0/0/0/15 the first if-statement results in True

answered May 5, 2021 at 16:02

funie200

3,9355 gold badges25 silver badges38 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

ForceBru · Accepted Answer · 2021-05-05 16:02:54Z

1

Let's visualise this:

'TenGigE0/0/0/0' in 'TenGigE0/0/0/0.12' is true, because 'TenGigE0/0/0/0' is a substring of 'TenGigE0/0/0/0.12':
```
TenGigE0/0/0/0.12
TenGigE0/0/0/0
```
'TenGigE0/0/0/1' in 'TenGigE0/0/0/1.46' is true, because 'TenGigE0/0/0/1' is a substring of 'TenGigE0/0/0/1.46':
```
TenGigE0/0/0/1.46
TenGigE0/0/0/1
```
Same for 'TenGigE0/0/0/15.55':
```
TenGigE0/0/0/15.55
TenGigE0/0/0/1
```

if statement executes the code after the first condition that is True, so even though 'TenGigE0/0/0/15' in 'TenGigE0/0/0/15.55' is True, 'TenGigE0/0/0/1' in 'TenGigE0/0/0/15.55' was first, so that's what got executed.

answered May 5, 2021 at 16:02

ForceBru

45k10 gold badges71 silver badges104 bronze badges

Comments

wjandrea · Accepted Answer · 2021-05-07 16:42:35Z

1

As already mentioned in other answers, '/1' is a substring of '/15'.

Another solution is to use regex with a word bound \b and a group for '0' OR '1':

import re

string = ["TenGigE0/0/0/0.12", "TenGigE0/0/0/1.46", "TenGigE0/0/0/15.55"]
for item in string:
    if re.match(r'TenGigE0/0/0/(0|1)\b', item):
        print("Yes")
    elif re.match(r'TenGigE0/0/0/15\b', item):
        print("cool")

Output:

Yes
Yes
cool

answered May 7, 2021 at 16:42

wjandrea

33.8k10 gold badges69 silver badges105 bronze badges

Collectives™ on Stack Overflow

Python - matching a string within a string explicitly

3 Answers 3

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related